1. Technical Field of the Invention
This invention relates to a connecting structure of a flat circuit member such as a flexible flat cable (hereinafter referred to as xe2x80x9cFFCxe2x80x9d) and a flexible printed circuit (hereinafter referred to as xe2x80x9cFPCxe2x80x9d), and more particularly to a connecting structure of a spiral cable used in a signal transmitting device for steering, for example, an automobile.
2. Related Art
As shown in FIGS. 9 and 10, an FFC (flat circuit member) 1 includes a plurality of parallel rolled conductors 2 (such as copper foils) held between covering films 3 and 4 by the use of an adhesive. An FPC (flat circuit member) has generally the same construction as that of the FFC 1, but differs therefrom in that conductors are formed by etching or plating.
One method of connecting such a flat circuit member to a wiring board is a method of connecting the FFC 1 as shown in FIG. 9. In this connecting method, the covering films 3 and 4, holding the conductors 2 therebetween, are removed over the same length from an end portion of the FFC 1, so that both sides of each conductor 2 are exposed over the same length. Then, the exposed conductors 2 are brought into contact respectively with a plurality of wiring terminal patterns 6 formed on a surface of a wiring board 5, and a heater tip 8 is brought into contact with the exposed conductors 2, thereby soldering these conductors.
A solder leveler 7 is formed on the surface of each wiring terminal pattern 6 over an entire length thereof. The solder leveler 7 is melted by heat transferred from the heater tip 8 through the conductor 2, and thereafter the solder leveler 7 is solidified to join the wiring terminal pattern 6 and the conductor 2 together, and also serves to prevent the oxidation of the connection portion. FIG. 10 is a plan view showing a condition in which the FFC 1 is joined to the wiring board 5, and FIG. 11 is a side-elevational view showing this condition.
FIG. 12 shows a related connecting structure in which the length of those portions of conductors 2, exposed by removing covering films 3 and 4 from an end portion of an FFC 1, is smaller than the length of wiring terminal patterns 6, and the covering films 3 and 4 overlap the wiring terminal patterns 6 at their end portions. In this structure, the length of solder levelers 7 is equal to the length of the exposed portions of the conductors 2 disposed at the end portion of the FFC 1.
In the above related flat circuit member-connecting structures, when each conductor 2 at the end portion of the FFC placed on the solder leveler 7 of the wire terminal pattern 6 is heated, the molten solder adheres to the entire lower surface of the exposed conductor 2 from which the covering film 3 is removed, so that the conductor 2 is soldered. However, when an external stress acts on an end portion 2a of the exposed conductor disposed adjacent to the end edges of the covering films 3 and 4, the stress concentrates on this conductor end portion 2a, which invites a problem that the conduction end portion 2a is liable to be cut.
Particularly when that portion of the FFC, covered with the covering films 3 and 4, is frequently subjected to bending and tensile stress because of the flexibility of the FFC 1, it is desired that the connection portion should have a sufficient durability to withstand such stress. For example, in the case of a flat circuit member (spiral cable) used in a signal transmitting device for steering an automobile, the FFC 1 is deformed in accordance with the rotation of a steering wheel, so that the swinging and pulling of the flat circuit member act on the connection portion. Therefore, it has been desired that the connecting structure of the flat circuit member, used in the steering signal-transmitting device, should be highly desirable.
It is therefore an object of this invention to provide a highly-reliable connecting structure of a flat circuit member in which a joint strength is increased, and the durability against an external stress is increased.
To achieve the above mentioned objects, according to a first aspect of the invention, there is provided a flat circuit member connecting structure comprising:
In this construction of the invention, the other covering film, overlying and covering the soldering region of the wiring terminal patterns, serves to reinforce the connecting boundary portion between the soldering region of the wiring terminal patterns and the flat circuit member.
According to a second aspect of the invention, in the flat circuit member connecting structure of the first aspect, the flat circuit member is a spiral cable used in a steering signal-transmitting device.
Therefore, in this invention, in addition to the above effects of the invention, the connecting strength of the opposite end portions of the spiral cable, used in the steering signal-transmitting device, is increased, thereby enhancing the reliability.
According to a third aspect of the invention, in the flat circuit member connecting structure of the first aspect, a solder leveler is formed on a surface of each of the wiring terminal patterns.
In this invention, the soldering leveler is formed on the surface of each wiring terminal pattern, and therefore in addition to the above effects of the invention, when the conductor is heated, heat transfers through the conductor, so that the exposed conductor is soldered to the soldering leveler disposed below the conductor.
According to a fourth aspect of the invention, in the flat circuit member connecting structure of the first aspect, each of the wiring terminal patterns is formed integrally with a wiring formed in a through hole formed through the wiring board.
In this invention, each wiring terminal pattern is formed integrally with the wiring formed in the through hole formed through the board, and therefore in addition to the above effects of the invention, even when an external stress is applied to the flat circuit member, this stress is received by the wiring terminal patterns and the wirings in the respective through holes, so that the wiring terminal patterns are prevented from separating from the board.
According to a fifth aspect of the invention, in the flat circuit member connecting structure of the fourth aspect, the wiring in the through hole is formed integrally with a wiring pattern formed on a reverse surface of the wiring board.
In this invention, the wiring in the through hole is formed integrally with the wiring pattern formed on the reverse surface of the board, and therefore in addition to the above effects of the invention, the effect of preventing the separation of the wiring terminal patterns is further enhanced. And besides, a connection member, such as a connector, can be electrically connected to the board, using the wiring patterns formed on the reverse surface of the board. Furthermore, since the wiring patterns are formed on that side of the board facing away from the soldering side, the wiring patterns are prevented from being affected by heat generated during the soldering operation.
According to a sixth aspect of the invention, in the flat circuit member connecting structure of the first aspect, a distal end of each of the conductors is covered with the first and second covering films.
Further to achieve the above mentioned objects, according to a seventh aspect of the invention, there is provided a flat circuit member connecting structure comprising:
According to an eighth aspect of the invention, in the flat circuit member connecting structure of the seventh aspect, an exposed length of each of the exposed conductors in the second covering film side is smaller than that in the first covering film side.